Archive for May, 2015

The damage to coral reefs varies of course. It’s greatest in the Caribbean and the Western Pacific – Indonesia, PNG, the Philippines, Guam. It’s least where humans can’t easily get to them – near isolated islands like Pitcairn and Easter, and around atolls scattered in the Pacific, hundreds of km from human communities.

A coral reef in the Philippines, reduced to rubble, similar to many in the Caribbean (wwf.org)

Pristine reefs, with angel fish, healthy corals, even top predators, are now very rare, exist isolated far from human communities (kidsdiscover.com)

And that variation is intriguing. If we reduced the stresses we can actually control – pollution, destruction and overfishing – will that make the reefs more resilient to the challenges of climate change? We can find out only by reducing those stresses.

Meanwhile, what happens to a reef, not wrecked by pollution and other destructive events, if overfishing is reduced? Will it recover any? some? all? of its lost ecological complexity? Marine Protected Areas (MPAs) that are large, old and isolated are recognized to be the ideal solution, but in much of the tropics where humans live in any abundance they are impractical, even impossible: completely restricting fishing is not an option.

Coral reefs of the world. Far too many people live far too close to far too many of them, for instance in the Caribbean and the Western Pacific (oceanservice.noaa.com)

Now a new and remarkable study indicates that some limited management can go a long way. We don’t have detailed long-term data on coral reefs to guide us, but we do now have current and recent data on a lot of reefs. A team of coral reef biologists has assessed what is known about the current status and recent history of 832 coral reefs, ranging from the most damaged to the most pristine (only 20 of the 832 are considered to be pristine).

The team compared fish biomass on the reefs – finding 1000 kg or more per hectare on a pristine reef, less than half that amount on overfished reefs, and as low as 10% of that amount on the most overfished reefs.

These illustrations are from the Nature article assessing 832 coral reefs. You will need to go to the article to see the details. a and b: The fish biomass of fished reefs is a small fraction of what exists on unfished reefs (red, extremely overfished; green, unfished). c: The less the fish biomass, the longer the time to full recovery if fishing is completely restricted – 50-60 years for the most damaged. d: With limited regulations in place, ecological complexity (functional return) gradually increases (nature.com),

Unexpectedly, limited regulations can still have considerable impact. For instance, protecting herbivorous grazers, scrapers and browsers (Parrot Fish come to mind) reduces algal cover, promotes coral dominance once again, and raises fish biomass. Eliminating the most damaging fishing gear, like beach seines, also helps fish recovery. Restricting access to the reef to those with negotiated rights to fish there while excluding external fishers helps even more. Sustainable fishing becomes possible.

Parrotfish (this is the Bicolor Parrotfish) are critical herbivores on a coral reef, sraping back algae (ecology.com)

Currently most reefs anywhere near human communities are hardly managed at all. Now we know that with limited regulations, a reef can recover to about half of its pristine fish biomass, and when it does, it is much less likely to collapse.

So sustainable fishing on somewhat recovered coral reefs is a target we can realistically aim for, an outcome so very clearly worthwhile in itself. These are grounds for a little optimism.

Will such changes then also make the reefs more resilient to the stresses of rising ocean temperatures and acidification associated with climate change? Coral reef biologists predict that they will, but though the theory is sound, it is untested.